Generally speaking, it is well known that there can be large temperature variations in the hot gases generated in a gas turbine engine. This is particularly true, circumferentially, at the entry to a turbine nozzle. As a result, there can be a significant circumferential variation in the temperature of the turbine exhaust flow.
By way of example, the temperature variation can often approach or even exceed 100.degree. F. Since it is important to avoid exceeding the safe maximum temperature permitted for the turbine of a particular engine, it has been common in the past to utilize thermocouples between turbine stages and/or to control engine operation by the measurement of exhaust gases. In this connection, exhaust gases have also commonly been measured by utilizing thermocouples.
In a conventional arrangement, a plurality of thermocouples are strategically positioned to measure the temperature of exhaust gases. This is illustrated, for instance, in Coar et al. U.S. Pat. No. 2,780,054 which provides a switch operable to permit a shut-off valve in a fuel meter to close in the event of excessive temperatures at the turbine discharge. In addition, a plurality of thermocouples could be utilized to provide an accurate average exhaust temperature for operating at optimal conditions.
As will be appreciated, this is one possible manner of dealing with the large temperature variations that typically occur in the hot gases generated in operation of a gas turbine engine. It is clear, however, that, while such an arrangement may function to control the temperature of gases entering the turbine nozzle so as to avoid exceeding the safe maximum for the turbine, it is very expensive and, even then, less then entirely reliable for a number of reasons. In order to avoid the expense, Peek Jr. U.S. Pat. No. 3,343,417 proposes the utilization of a probe that includes a plurality of openings and scoops into which exhaust gas flows.
In the Peek Jr. '417 arrangement, the openings and scoops are provided for the purpose of sensing an average of the exhaust gas temperature. This is said to occur because the scoops are uniformly spaced. Unfortunately, Peek Jr. U.S. Pat. No. 3,343,417 depends upon ideal operating conditions not found in gas turbine engines in actual practice.
More specifically, Peek Jr. '417 proposes a technique which clearly cannot assure averaging of exhaust gas temperatures. The single temperature probe, while extending diametrically of the exhaust duct, is incapable of accounting for the significant circumferential variations in temperature normally encountered. Moreover, Peek Jr. '417 would not be capable of giving a reading that could be calibrated in relation to the mean turbine inlet temperature.
The present invention is directed to overcoming one or more of the foregoing problems and achieving one or more of the resulting objects.